Heretofore, metering rods for carburetors have been provided with coil torsion springs to urge the metering rods into engagement with a side of a metering orifice. As metering rods have moved generally a limited vertical direction the torsion spring has provided a generally uniform force to the metering rod for the short travel of the metering rod. An example of a type of coil torsion spring employed for this purpose is illustrated in U.S. Pat. No. 1,961,747 dated June 5, 1934, in which a vertically movable metering rod has a torsion spring applying a constant force to the metering rod regardless of the position of the metering rod.
It is desirable to maintain a metering rod in contact with the surface defining the orifice in order to maintain a generally uniform fuel flow for a specific orifice cross section. As a practical matter, it is very difficult to hold a rod in the center of the orifice and if this could be accomplished, the flow would remain constant, but there is no practical or convenient means of doing this. Heretofore, such as shown in U.S. Pat. No. 1,961,747, coil springs have been provided to continuously urge a metering rod into engagement with a side of an orifice. With metering rods that move vertically, a generally uniform force has been applied to the metering rod during its entire movement by such torsion spring and the force urging the metering rod into engagement with the side of the orifice plate could be easily predetermined and maintained.